Purpose
The aim of this study was to evaluate, using a rabbit model, the little-known effect of different levels of peak inspiratory flow on acutely injured lungs.
Methods
Fourteen male rabbits (body weight, 2711 ± 146 g) were anesthetized and their lungs were injured by alveolar overstretch with mechanical ventilation until PaO 2 was reduced below 300 mmHg. Injured animals were randomly assigned to: the P group—to receive pressure-regulated volume-control ventilation (PRVCV; n = 7); and the V group—to receive volume-control ventilation (VCV; n = 7). Other ventilator settings were: fraction of inspired oxygen (FIO 2), 1.0; tidal volume, 20 ml·kg−1; positive end-expiratory pressure (PEEP) 5 cmH2O; and respiratory rate, 20 min−1. The animals were thus ventilated for 4 h. Throughout the protocol, ventilatory parameters and blood gas were measured every 30 min. After the protocol, the lung wet-to-dry ratio and histological lung injury score were evaluated in the excised lungs.
Results
Throughout the protocol, peak inspiratory flow and mean inspiratory flow values in the P group were significantly higher than those in the V group (26.7 ± 5.0 l·min−1 vs 1.2 ± 0.2 l·min−1, and 4.3 ± 0.3 l·min−1 vs 1.1 ± 0.1 l·min−1; P < 0.05). The wet-to-dry ratio in the P group was also significantly higher than that in the V group (7.7 ± 0.9 vs 6.3 ± 0.5; P < 0.05). More animals in the P group than in the V group had end-of-protocol PaO 2/FIO 2 ratios below 200 mmHg (43% vs 0%; P = 0.06).
Conclusion
In rabbits with injured lungs, high peak inspiratory flow with high tidal volume (VT) reduces the PaO 2/FIO 2 ratio and increases the lung wet-to-dry ratio.